[v3,0/5] rkisp1: Allow usage of more than 4 buffers

23838 mbox series

Hi all,

In the rkisp1 pipeline the value of StreamConfiuration.bufferCount is
reset to 4 on validate(). This effectively limits the number of buffers
that are in the loop to 4. As soon as the consumers
(gstream/pipewire...) of the buffers need more than 1 buffer at a time,
we start to see frame drops. Sven resurrected an old series [1] that
solves the issue at the expense of an additional control and breaking
changes in the API.

In the IoB code camp two weeks ago there were some discussions regarding
improvements in the rkisp1 regulation and per-frame-control (PFC). PFC
has been an ongoing topic for quite some time now and it seems to slowly
converge. Still we were hesitant in breaking the API or introducing new
controls before the overall concepts have stabilized enough.

To mitigate the pain mentioned above we came up with a minimal changeset
that allows to request more than 4 buffers. Only 4 (or the pipeline
depth reported by the pipeline) buffers are queued into the device.
This has the same benefits as [1] but doesn't require an API break.

Updates in Version 1 of the series (after the RFC):
- Included the feedback from reviews of the RFC (For etails see the chaneglog in
  the individual patches)
- Included two patches with fixes from Sven an Kieran
- I modified patch (6/6) from Kieran a bit after the review comment from
  Laurent. @Kieran could you have a look at that as I don't have a easy way to
  replicate the issue? Ideally I would like to merge that patch into patch 2/6
  as it fixes an issue introduced there. For now I left it separate for easier
  review.

Updates in v2:
- Fixed segfault due to wrong lambda capturing
- Fixed ASSERT dues to recursive call of doQueueRequests in virtual pipeline
- Improved documentation
- Squashed patch 6 into patch 2

Updates in v3:
- Split kPipelineDepth into kRkISP1MaxQueuedRequests and kRkISP1MinBufferCount.
  These contain the same value but convey the intent better and make the code
  clearer.
- Ensure the bufferCount is reset to at least 4 in validate.
- Fixed the underallocation of V4L2 buffer structs as proposed by Kieran
- Incorporated some stylistic suggestions from review

Best regards,
Stefan

Nícolas F. R. A. Prado (1):
  libcamera: pipeline: rkisp1: Don't rely on bufferCount

Stefan Klug (4):
  libcamera: pipeline_handler: Move waitingRequests_ into camera class
  libcamera: pipeline_handler: Allow to limit the number of queued
    requests
  pipeline: rkisp1: Limit the maximum number of buffers queued in
  pipeline: rkisp1: Properly handle the bufferCount set in the stream
    configuration

 include/libcamera/internal/camera.h           |  2 +
 include/libcamera/internal/pipeline_handler.h |  9 ++-
 src/libcamera/camera.cpp                      |  9 +++
 src/libcamera/pipeline/rkisp1/rkisp1.cpp      | 42 ++++++++---
 src/libcamera/pipeline/rkisp1/rkisp1_path.cpp |  7 +-
 src/libcamera/pipeline/rkisp1/rkisp1_path.h   |  4 +-
 src/libcamera/pipeline_handler.cpp            | 72 +++++++++++++++----
 7 files changed, 106 insertions(+), 39 deletions(-)